Microelectronic devices, such as memory devices and microprocessors, typically include a microelectronic die encased in a protective covering. The die can include memory cells, processor circuits, interconnecting circuitry and/or other functional features. The die also typically includes an array of very small bond-pads electrically coupled to the functional features. When the die is packaged, the bond-pads are coupled to leads, solder ball-pads or other types of terminals for operatively coupling the microelectronic dies to buses, circuits and/or other microelectronic devices.
Several different techniques have been developed for packaging microelectronic dies. The dies, for example, can be incorporated into individual packages, mounted with other components in hybrid or multiple chip modules, or connected directly to a printed circuit board or other types of substrates. When a die is incorporated into an individual package, the bond-pads on the die are typically coupled to a lead frame, and the die is covered or otherwise sealed from the environment. When the die is attached directly to a printed circuit board or another type of substrate, the bond-pads on the die are typically coupled to corresponding contact elements on the substrate using wire-bond lines, ball grid arrays and other techniques. The dies that are mounted directly to the substrates are generally Chip Scale Package devices (CSP) or Flip Chip Bare Die devices (Flip-Chip).
CSP and Flip-Chip devices generally have one or more protective casings that encapsulate the dies and any exposed contact elements, bond-pads or wire-bond lines. The protective casings should shield the die and the other components on the substrate from environmental factors (e.g., moisture), electrical interference, and mechanical shocks. The protective casings are accordingly robust elements that protect the sensitive components of a microelectronic device. The protective casings are generally composed of plastics, ceramics, or thermosetting materials.
One conventional technique for fabricating the protective casings involves placing the die in a cavity of a mold, and then injecting a thermosetting material into the cavity. The thermosetting material flows over the die on one side of the substrate until it fills the cavity, and then the thermosetting material is cured so that it hardens into a suitable protective casing for protecting the die. According to conventional practices, the protective casing should not have any voids over the die because contaminants from the molding process or environmental factors outside of the mold could damage the die. The thermosetting material, moreover, should not cover a ball-pad array on the substrate or damage any electrical connections between the die and the substrate. Therefore, according to conventional practices, the thermosetting material should be molded in a manner that avoids (a) producing voids in the protective casing, (b) covering certain portions of the substrate with the thermosetting material, and (c) displacing or otherwise damaging any wire-bond lines or solder joints between the die and the substrate.
One drawback of packaging microelectronic devices is that during high-temperature processing cracks or voids can form in the protective casing, or the protective casing can delaminate from the substrate. Such cracking or delamination, for example, may occur during a solder reflow procedure in which the packaged microelectronic devices are quickly heated to reflow solder balls and/or or solder paste pads. This problem is particularly noticeable in procedures that quickly heat the packaged devices to an elevated temperature. When the casing of a packaged microelectronic device cracks or delaminates from the substrate, the device is often rejected because such cracks or voids can expose very delicate components (e.g., bond-pads or wire-bond lines) to external environmental factors. It will be appreciated that such cracking of the casing results in extremely expensive losses because it occurs at the end of the fabrication process after a significant amount of money has been expended to manufacture each packaged microelectronic device. Therefore, it would be desirable to develop an apparatus and method for reducing or completely preventing the casing from cracking or delaminating from the substrate during high temperature processing.